1. Field of the Invention
The present invention relates to a battery remaining amount warning apparatus used for a digital camera.
2. Description of the Related Art
As a conventional method for warning about a remaining amount of a battery of an electronic device, it is a general practice that a battery voltage is measured and a warning about the remaining amount is issued when the battery voltage falls below a specified value or DC resistance of the battery increases.
There are a variety of types of battery such as alkaline cell, nickel hydrogen cell, nickel cadmium cell, and there are also a variety of battery characteristics. However, with a monitoring of the battery voltage alone, depending on the type of the battery, the battery power may not be used to the full because a considerable amount of the battery can still be used after the warning is given about the insufficient remaining amount of the battery.
Furthermore, when the remaining amount of the battery is predicted from the battery voltage, the voltage varies depending on the type of the battery and when the battery voltage is low because of the nature of the type of the battery, a warning is issued earlier. For example, a warning is issued with an alkaline cell at 1.5 V/cell and with a NiCd cell at 1.2 V/cell.
To solve this problem, there is also a proposal of a method for measuring a battery voltage by providing a dummy-load circuit (Japanese Patent Publication No. 63-3538). However, this method increases unnecessary power consumption.
There is also a proposal of a method for deciding whether a camera operates normally or not based on a boosting operation of a booster circuit when a flash capacitor is charged (Japanese Patent Application Publication No. 2000-56370), but when no flash is used or can be used, there is no way to decide it.
Digital cameras are becoming widespread today. Their batteries are however likely to run down quickly when a liquid crystal monitor or drive system is used frequently.
In order to use battery power to the full and avoid the battery from running down while a digital camera is operating, a conventional camera shows a remaining amount of the battery and gives a warning when the camera is continuously used in a mode under operation such as a recording mode, playback mode and flash charge mode.
However, since a digital camera has various modes using different supply currents such as playback, recording and flash charge, etc., there are various cases, for example, flash charge is not possible while recording without flash is possible or recording is not possible while playback is possible. In such cases, it would be convenient if the user can select a mode according to the remaining amount of the battery and this will prevent the battery from running down during operation.